1. Field of the Invention
The present invention relates to thin film heads for magnetically writing information on data storage media, and particularly to fabrication processes for manufacturing such heads. Still more particularly, the invention concerns the reduction of write head feature size beyond that which can be achieved using conventional photolithography.
2. Description of the Prior Art
By way of background, thin film magnetic write heads for use in data storage devices, such as disk drives, conventionally include features such as P1 and P2 pole pieces that cooperate to record magnetic domains in concentric track patterns on an underlying data storage medium. The configuration of the pole pieces, and particularly the track width feature size, is an important determinant of the track width of the magnetic domains recorded on the underlying medium. Because narrow track width translates to increased data storage capacity, all other things being equal, it is a design goal of disk drive manufacturers to reduce the track width feature size of the pole pieces.
In thin film magnetic head processing, features are constructed using photolithographic processes. For example, to fabricate a pole piece, a photoresist layer is formed, then photo-exposed using a photolithographic mask to define the pole piece geometry, and then photo-developed to form a trench conforming to the defined geometry. The metallic pole piece material (typically a nickel-iron alloy) is deposited in the trench using an electroplating process. The remaining photoresist material is then stripped away, leaving behind the fully formed pole piece. In a tri-layer resist process, a feature is formed in a polymer layer using a xe2x80x9chardmaskxe2x80x9d layer over the polymer material. A standard photoresist layer is spun onto the hardmask and patterned to define the desired etch mask. Two etching processes are used to first etch the hardmask and then the polymer layer. The function of the hard mask is to ensure that the feature is formed anisotropically in the polymer layer during the second etching phase.
The problem with this type of processing is that feature size can only be narrowed photolithographically by using shorter wavelength light and contrast enhancement techniques. Thus, whether conventional photolithography is used, or newer technologies such as deep UV or electron beam lithography, reductions in feature size typically require new and more expensive light sources and exposure technology. An additional disadvantage of photolithographic solutions is that line edge roughness becomes a concern as photolithographic features become ever smaller.
Accordingly, an improved technique for reducing feature size in a thin film magnetic write head is required if improvements in disk drive performance are to be achieved. What is particularly needed is a new technique whereby feature size can be reduced while using any thin film magnetic head photolithographic process, including deep UV or electron beam lithography, without having to invest in higher cost photolithographic resolution enhancement solutions. An additional desirable requirement is that the technique be compatible with a tri-layer resist process in which a hardmask and an underlying polymer layer are separately etched to define features. A further requirement is that of reducing the line edge roughness of the photolithographically defined trenches.
The foregoing problems are solved and an advance in the art is obtained by a novel isotropic deposition method for trench narrowing of thin film magnetic write head features to be created by reactive ion etching. According to the method, a polymer base layer is formed on a substrate, such as an electroplating seed layer. A hardmask layer (hardmask) is applied onto the polymer layer and a photoresist imaging layer is spun onto the hardmask to a desired thickness. A trench is defined in the photoresist layer to form a pattern for the feature. The trench is deep enough to expose the hardmask, and has substantially vertical side walls. Following formation of the trench, a spacer layer is deposited isotropically or directionally at an angle to cover the trench side walls. The material used to form the spacer layer is one that can be deposited isotropically while preserving trench geometry, or directionally at an angle. The material must also be etchable by a subsequent hardmask etch process and resistant to a subsequent base layer etch process.
Horizontal portions of the spacer layer that overlie the bottom of the trench (if any) are anisotropically etched as part of the hardmask etch process to remove such material. Hardmask material is also removed from the trench bottom to expose the polymer layer. Vertical portions of the spacer layer that cover the trench side walls are left intact. This process initiates the formation of a narrowed trench that is reduced in horizontal size according to approximately twice the thickness of the spacer layer as deposited on the trench side walls.
The base layer etch process extends the trench anisotropically through the polymer layer to reveal the underlying substrate. This is done without removing the spacer layer material from the trench sidewalls, so that the narrowed trench size is carried through the polymer to the substrate. A feature, such as a metallic pole piece, may now be formed by electroplating metallic material into the narrowed trench.